As described in European patent 0,447,818 of K. Claar et al (claiming priority of German 4,008,834 of 20 Mar. 1990) it is known to provide an electrical switch that is directly actuated by the key cylinder of a motor-vehicle latch. The key can only be inserted into and withdrawn from the cylinder in a center starting position. Pivoting the key in one direction locks or unlocks the door and, in a central lock system, operates all the other door latches also. Pivoting the key in the opposite direction from the starting position enables the antitheft mode that not only locks all the latches, but also disables any other elements, for instance inside door buttons, that could be used to open a door.
In this Claar patent the switch is a simple mechanical one, having a center position corresponding to the starting position for the cylinder and two oppositely offset end positions. It has been suggested in German utility model 9,415,257 to replace the mechanical switch with a semiconductor hall-effect system to eliminate the need for physical contact between the various parts and thereby increase the service life of the device. Such a system, however, is fairly complex and is also susceptible to manipulation by a would-be thief equipped with a powerful permanent magnet. Such a magnet is simply positioned on the door adjacent the hall-effect arrangement to actuate its sensors and thereby operate the latch.